Age at first reproduction has declined markedly in cod the last decades (Figure 4.6.6). This may have considerable consequences for cod recruitment and the role of cod as a top predator in the ecosystem. In the 1940s, a cod typically reproduced for the first time when it was between 9 or 10 years old. In the 1990s, average age at first reproduction had declined to between 6 and 7 years.
Re-reading of old cod-otholits suggests that age had been over estimated in the beginning of the time series in the above figure, and that the decline in age at maturity therefore has been less pronounced than suggested here (Zuykova et al 2009).